The One Ring’s inscription is written in Tolkien’s Black Speech.
The inscription begins, “Ash nazg durbatulûk,” translated as “One Ring to rule them all.” Tolkien created the Black Speech for Sauron and associated it with Mordor, making it distinct from the Elvish languages used elsewhere in his legendarium.
Readers often mistake the inscription for Quenya or Sindarin because those Elvish languages are among Tolkien’s best-known creations. The ring poem, however, is presented in multiple languages: the inscription itself uses Black Speech, while the surrounding verse is translated into English in The Lord of the Rings.
The language was designed to sound harsh and commanding. Tolkien gave less surviving vocabulary for Black Speech than for languages such as Quenya and Sindarin, but the Ring inscription remains its most famous example.